The present invention particularly pertains to a microactuator device for use in a multiple track disk drive system so that fine positioning of a transducing head over a selected track of the disk may be obtained, and more particularly, to a piezoelectric microactuator device that provides a simplified, low-cost construction when compared with the prior art designs.
Magnetic disk drives are information storage devices that use thin film magnetic media to store data. A typical disk drive as seen in FIG. 7 of U.S. Pat. No. 6,166,890, the disclosure of which is incorporated herein, includes one or more rotatable disks having concentric data tracks in which data is read or written. As a disk rotates, a head transducer, also referred to as a magnetic recording head, is supported by a slider and positioned by an actuator element to magnetically read data from, or write data to, various tracks on the disk. Typically, the head transducer is attached to a slider having an air-bearing surface, which is supported adjacent to a data surface comprising the data tracks by a film of air generated by the rotating disk. Suitable wires connect the transducer on the slider to a data processing unit that controls read/write electronic circuitry. The spacing between data tracks continues to decrease with increase in recording density, requiring greater precision for head positioning. External and internal disturbances in a disk drive continuously move the head transducer off the data track. Conventional disk drives correct for off-track motion by actuating the arms carrying the head transducers using a voice coil motor. See the Figures of U.S. Pat. No. 6,115,223, the disclosure of which is incorporated herein by reference. However, a voice coil motor lacks fast response and sufficient resolution for small motions required to effectively maintain position of the transducing head on a track of a high-track density disk. Therefore, a secondary fast response high-resolution head positioning mechanism is necessary for small motions to reduce track registration error in high-density disk drives.
Various prior art piezoelectric microactuator designs correct for hard disk drive disk track misregistration. These include designs with piezoelectric microactuators mounted on the arm, or on the suspension near hinge, or near or under the slider carrying the head transducer. Designs piezoelectric microactuators mounted on the arm produce highest slider movement but excite undesirable voice coil motor coil, arm and suspension load beam modes. Designs with piezoelectric microactuators mounted near the hinge produce medium slider movement but excite undesirable arm tip and suspension modes. Designs with piezoelectric microactuators mounted near the slider produce small slider movement but excite minimum undesirable modes of flexure and load beam. Location of piezoelectric microactuators shall depend on a drive configuration and requirement.
The prior art Japanese patent 63-291271 has a piezoelectric element (formed by cutting a U-shape through groove in a piezoelectric material plate) mounted under and concentric to the slider and appears to provide translation motion along the long axis of the suspension more suitable for linear and not rotary actuators. Present invention differs in configuration of piezoelectric element provides rotary motion and intended for use with rotary actuators.
U.S. Pat. No. 5,856,896 (“'896 patent”) teaches the use of two parallel piezoelectric elements on the leading edge of the slider attached to a suspension. It further teaches the use of a compliant shear layer connecting the slider and the suspension. The design of the '896 patent has the disadvantage of using two piezoelectric elements instead of a single element. The design must also deal with fatigue problem related to the compliant layer. Japanese references JA 0097174 and JP 10-027446 also teach the use of two piezoelectric elements polarized in opposite direction and placed under the slider for angular motion. However, normal placement inaccuracies associated with the use of two piezoelectric pieces could result in asymmetrical loading, which in turn could result in undesirable dynamic modes. Also, accurate placement and bonding of two piezoelectric microactuators instead of one is more expensive. Present invention solves these problems by having a simple single element that is polarized in only one direction and placed accurately at slider center.
U.S. Pat. No. 6,166,890 discloses the mounting of the piezoelectric microactuators in the same plane and near the slider. The problem with this approach is that the design has a more complex mechanism like a cradle, is more fragile, excites more undesirable dynamic modes, and is more expensive to manufacture.